A test cross is performed to distinguish between

Options

A. two homozygous forms
B. Two heterozygous forms
C. a homozygous dominant and a heterozygous form
D. a homozygous recessive and the heterozygous form

Answer

To solve the question about what a test cross is performed to distinguish between, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Test Cross**: A test cross is a genetic cross used to determine the genotype of an individual with a dominant phenotype but unknown genotype. This is typically done by crossing the individual with a homozygous recessive individual.

2. **Identify the Options**: The options given are:
- (A) Two homozygous forms
- (B) Two heterozygous forms
- (C) A homozygous dominant and a heterozygous form
- (D) A homozygous recessive and a heterozygous form

3. **Analyzing Each Option**:
- **Option A**: Two homozygous forms would not help in determining the unknown genotype since both parents would have known genotypes.
- **Option B**: Two heterozygous forms would also not clarify the genotype of the unknown parent because both could produce the same dominant phenotype.
- **Option C**: A homozygous dominant and a heterozygous form would not provide clarity since both would show the dominant phenotype.
- **Option D**: A homozygous recessive and a heterozygous form is the correct choice. The homozygous recessive parent will only express the recessive phenotype, allowing us to determine the genotype of the heterozygous parent based on the offspring's phenotypes.

4. **Conclusion**: The correct answer is **Option D**: A homozygous recessive and a heterozygous form.